The use of an implanted internal prosthetic device to repair dysfunctional tissues in the skeletal system poses complex biomechanical challenges. One challenge is achieving a mechanically competent fixation of the device to the biological tissue at the reconstruction site. Fixation strength should be adequate to withstand loads encountered in vivo during the immediate post-operative period as well as during long-term progressive rehabilitation. Post-operative loads are generally managed by immobilization protocols in order to allow fixation strength to develop coordinately with the repair process. Rehabilitative loads are typically applied once the repaired structure attains sufficient mechanical competence. An effective fixation strategy should be able to achieve immediate fixation during the surgical procedure to maintain the proper positioning of the device during the repair phase and should be able to promote effective integration into the repairing tissue with sufficient fixation strength and functional longevity to allow for tissue ingrowth, such as, for example, neo-tendon or neo-ligament growth.
Current methods for attachment of a graft or bioprosthesis to bone involve drilling, insertion and fixation with adhesives or mechanical fasteners such as interference screws, anchors or buttons. Surgical repair of avulsed tendons and ruptured ligaments often requires joining fibrous biomaterials to bone. Sutures can be used to join the ends of avulsed tendons to bone, and they are fixed in place with bone anchors or buttons, both of which typically require drilling bone tunnels. Tendon autografts are used for anterior cruciate ligament repair, and these are fixed within bone tunnels with interference screws. These fixation approaches have limitations due to one or more of a variety of factors, including invasiveness, the use of non-biological materials, and a propensity of the device to fail with time that is thought to be associated with micro-motion of the bioprosthesis in the bone insertion site. See, e.g., Silva et al, The insertion site of the canine flexor digitorum profundus tendon heals slowly following injury and suture repair. J. Orthop. Res. 20:447-453, 2002; Rodeo et al, Tendon healing in a bone tunnel. A biomechanical and histological study in a dog. J. Bone Joint Surg. (AM) 75:1795-1803, 1993; and Greis et al, The influence of tendon length and fit on the strength of the tendon-bone tunnel complex, Am. J. Sports Med. 29:493-497, 2001. In addition, fixation of biomaterials for tendon and ligament repair in children presents an additional challenge in that these fixation strategies utilize bone tunnels that may traverse the growth plate, creating potential problems for skeletal growth.